Storage projection tube



M. VON ARDENNE STORAGE PROJECTION TUBE Filed Nov. 29, 1959 March 17, 1942.

INVENTOR MANFRED VONA-RDENNE ATTORNEY Patented Mar. 11, 1942 STORAGE PROJECTION TUBE Manfred von Ardennc, Berlin, Germany Application November 29, 1939, Serial N0.-306,610

' In Germany November 14, 1938 2 Claims. (c1. ire-1.5)

This invention relates to an improvement in television receiving tubes of the cathode ray type wherein a projected image may be produced.

" optimum qualities. Theimprovements obtain- Examples of such tubes are shown and described in my patent applications Serial #292,017 filed August 16, 1939, and Serial #307,573, flledDec. 5, 1939.

In these applications, and particularly in the first named application, cathode ray tubes have been disclosed in which, by, the aidof polarized light, charge distributions are rendered visible upon (piezo-electric) crystal screens r surfaces. In research work done with diflerent types of crystals and crystal sections (as disclosed in the application Serial #307,573) it has been shown that the doubling of the electro-optic ell'ect theoretically is to be expected. Furthermore, in an arrangement discussed in application Serial #292,017, a reflecting (mirroring) crystal layer may be conveniently used in practice. It has been ascertained that with potentials of an order of magnitude of 5000 volts extremely strong or bright images have been produced, sufllcient to carry into practicearrangements of the invention with moderately elaborate (circuit) means. However, in connection with the said practical experiments, a certain disadvantage and difliculty,

was found'to exist in the arrangements previously disclosed which is to be obviated by the invention disclosed herein.

It has been found that the secondary emission properties which are present when the crystal type is fixed, and when the crystal surface is di rectly struck by electrons, is extremely undesirable. particular it has been found that even with higher potentials (say, above 5000 volts) a stronger secondary emission is present, with the result that the charging of the crystal surface required for the creation of light control necessitates the use of extraordinarily high voltage electron beams. the present application to obviate the use of high voltage beams, and it has been found to be essentially more advantageous to coat or film the crystal screen, upon the face thereof turned towards the scanning electron beam, with a very tenuous skin or layer of optical cleamess. The secondary electron emissive characteristic of this film or skin may be adapted to the requirements in electrical respect. It is then feasible to choose and make the crystal screen only on the basis of the optimum size or value of its electro-optic eifect, regardless of charging and storing conditions, while, inversely, the electronic circuit of In the case of zinc blende (sphalerite) in Accordingly, it is the object of the receiving tube can be chosen so asto possess able by separating the two conditions according to the present invention, as may be inferred from what 'precedes, result primarily in a reduction of the anode or accelerating potential for the scanning cathode ray beam, andthus in an appre- I ciab'le saving in circuit means.

The present invention may be best understood by referring to the drawing, wherein:

Figure 1 represents the present invention as applied to a television receiving tube-of the projection type, and I Figure 2 shows a detailed enlargementof the crystal plate.

In the drawing, and particularly in Figure 1 thereof, is shown a cathode ray tube 2 in which is positioned a gun structure III for producing a narrow focused beam of electrons. The intensity Y of the beam of electrons is determined by the potential of the control electrode I2. Also positioned in the tube is a crystal plate which comprises a support plate 22, a' layer of crystals 20,

and a layer or film of transparent material 20 which has a predetermined secondary electron emissive characteristic. Positioned in front of the crystal plate is an electron accelerating screen 52, for producing rapid acceleration of the electrons which constitute the beam in the vicinity of the crystal plate. The cathode ray deflecting means l8 and I8 respectively.

A source of light 36 is provided, and the light which originates from the source is directed to ward the receiving tube by means of the reflector 34. The light is passed through a lens 38 and a polarizing screen 46 before being projected upon the crystal plate 20. Positioned on the other side of the receiving tube is a still further polarizing screen 48 and lens. system 40, in order to focus the produced optical image upon a receiving screen II in an anlarged manner.

As described in the above mentioned application, the amount of light which is permitted to pass through the crystal plate is determined by and intensified television image is reproduced.

The crystal plate is shown in detail in Figure 2 and as stated above, includes a support 22 upon which is positioned a layer of crystals 20 which may be prepared and arranged in the manner suggested in application Serial No. 307,573, referred to above. The layer 26 which is preferably light transparent and which has a predetermined secondary emissive characteristic, is attached to the layer of crystals 20 by means of cement or some other adhesion material 24. The thickness of the material 24 should be maintained as thin as possible yet sufliciently thick to ensure close contact between the layer or film 26 and the crystal layer 20.

The layer or film 26 which is applied upon the anterior face of the crystal plate, for electrical and optical reasons, is so applied that there exists optical contact between the surface of the layer and the crystal layer 20. If necessary, such contact may be obtained by means of a clear transparent substance 24 which will be stable in vacuum, such as, for instance, a waterglass. The layer 26 must possess high insulating qualities and may consist of a glass or vitreous layer. Alternatively, mica platelets or scales of similarly clear transparent substances may be used. The thickness of the film or layer 26 should be maintained as thin as possible, and it is only necessary that its thickness be suflicient to exceed the depth to which the scanning cathode ray beam penetrates the layer. Excessive thicknesses of the layer should be avoided, for, on the one hand, this would tend to enlarge the smallest possible picture unit diameter, and on the other hand, the electro-optically active field intensity would be diminished. The thickness of the layer 26 should therefore be determined in accordance with the intensity of the scanning cathode ray beam which is to be used in the tube.

When the film or layer 26 is made, for instance, from standard glass stock, the secondary emissive characteristics increase gradually with increase in beam accelerating potential until a value of unity is reached, when the accelerating potential is between 3000 and 5000 volts. Since a secondary emission ratio of greater than unity is desired, and preferably since it is desirable to operate the beam at such potential as to produce maximum secondary emission, secondary anode I accelerating potentials of the order of from 8000 to 15,000 volts may be necessary, depending upon whether the light is to be transmitted through the crystal once, or whether a reflection arrangement is to be used and the light is transmitted through the crystal twice, as suggested in Figure 12 of application Serial #292,017.

In order to produce tubes with any degree of uniformity, it is necessary that the secondary emissive properties of the film or layer 26 be maintained as uniform as possible, and in order to maintain such uniformity, great care must be exercised in initially preparing the surface oi! the layer of crystals 20 and also in determining the thickness of the cementing substance 24, as well as the thickness of the layer 26.

From the above it may be seen that a new and improved television receiving tube of the projection type has been developed, and that through the use of such a tube very enlarged and intense television images may be produced.

' Various alterations and modifications may be made in the present invention without departing from the spirit and scope thereof, and it is desired that any and all such modifications be considered within the purview of the present invention except as limited by the hereinafter appended claims.

I claim:

1. A television receiving system comprising a cathode ray tube having means therein for generating a beam of electrons, a target area, means for deflecting the beam oi electrons to cause the same to scan the target area, said target area comprising a transparent support base, a layer crystals of substantially uniform thickness positioned on said base, and a translucent film of insulating material positioned upon the crystal layer, said fllm of material having a predetermined uniform secondary electron emissive characteristic whereby charge conditions are produced on the target area as a result of the scanning operation, means for directing polarized light upon the target area, and means including a polarizing screen for focusing the polarized light transmitted through the target area upon an image screen whereby an image may be produced upon the image screen in accordance with the rotation of the plane of polarization of the crystal layer as a result of modulations of the scanning cathode ray beam.

2. A television system comprising a cathode ray tube, a target area in said tube, means including a gun structure for producing a focused beam of electrons and for directing the same against said target area, means for deflecting the cathode ray beam in mutually perpendicular directions to scan the target area, said target area comprising a translucent conducting support base, a crystal layer of zinc blende positioned upon the support base, said crystal layer having a variable plane of polarization in accordance with the electrostatic potential impressed thereon, a film of insulating material attached to the crystal layer, said film having a predetermined uniIorm secondary electron emissive characteristic of a ratio greater than the unity whereby charge conditions are produced on the target area as a result of the scanning operation, means for directing polarized light upon the target area. and means including a polarizing screen for focusing the light transmitted through said target area upon an image screen whereby an optical image may be produced on the image screen in accordance with the rotation of the plane of polarization of the crystal layer as a result of modulations of the scanning cathode ray beam.

MANFRED VON ARDENNE. 

